In a switching converter, the switching elements generate large power bounce, ground bounce and switching noise when the switching elements turn on and turn off. The switching noise is mixed with signals through power lines and substrate and some common block, for example bandgap reference generator and comparator. If switching noise is superimposed on an analog signal that represents a sensing signal and the signal is sensed in this load state, the controller will be fault function. The fault function could be that the switching elements of other power switching converters turn on and turn off at the wrong timing.
FIG. 1 shows a conventional multi-channel switching converter 100 including several channels 106, 108, . . . , 110. In the first channel 106, transistors MH1 and ML1 are serially connected between a power line VIN and a ground line or substrate GND, a driver 116 generates signals U1 and L1 according to a pulse-width modulation (PWM) signal PWM1 to switch the transistors MH1 and ML1 so as to generate an output voltage VOUT1, voltage divider resistors R1 and R2 divide the output voltage VOUT1 to generate a feedback signal FB1, a current sensor 118 detects the current flowing through the transistor MH1 to generate a current-sensing signal ISENSE1, and a controller 114 generates the pulse-width modulation signal PWM1 according to the feedback signal FB1 and the current-sensing signal ISENSE1. In the second channel 108, transistors MH2 and ML2 are serially connected between the power line VIN and the ground line or substrate GND, a driver 122 generates signals U2 and L2 according to a pulse-width modulation signal PWM2 to switch the transistors MH2 and ML2 so as to generate an output voltage VOUT2, voltage divider resistors R3 and R4 divide the output voltage VOUT2 to generate a feedback signal FB2, a current sensor 124 detects the current flowing through the transistor MH2 to generate a current-sensing signal ISENSE2, and a controller 120 generates the pulse-width modulation signal PWM2 according to the feedback signal FB2 and the current-sensing signal ISENSE2. In the N-th channel 110, transistors MHN and MLN are serially connected between the power line VIN and the ground line GND, a driver 128 generates signals UN and LN according to a pulse-width modulation signal PWMN to switch the transistors MHN and MLN so as to generate an output voltage VOUTN, voltage divider resistors R5 and R6 divide the output voltage VOUTN to generate a feedback signal FBN, a current sensor 130 detects the current flowing through the transistor MHN to generate a current-sensing signal ISENSEN, and a controller 126 generates the pulse-width modulation signal PWMN according to the feedback signal FBN and the current-sensing signal ISENSEN.
In the converter 100, the multiple channels 106, 108, . . . , 110 are integrated in a single chip 102 and all the channels 106, 108, . . . , 110 share the common power line VIN as well as the ground line or substrate GND. Package inductances Lp1, Lp2, . . . , LpN are resulted from bouning wires, and package inductances Lg1, Lg2, . . . , LgN are resulted from bouning wires between the ground line GND and the transistors ML1, ML2, . . . , MLN, respectively. Due to the switching of the transistors MH1, ML1, MH2, ML2, . . . , MHN, MLN in the channels 106, 108, . . . , 110, power bounce and ground bounce are produced and mutually interfere each other therebetween through the common power line VIN as well as the ground line or substrate GND. The power bounce and ground bounce are also known as switching noise, and in addition to the common power line VIN and the ground line or substrate GND, they may also introduce mutual interference between the channels through some other common elements, for example bandgap reference generator and comparator.
FIG. 2 is a partially enlarged view of the channel 106, and FIG. 3 is a waveform diagram of the current I1 and voltage V1 on the package inductance Lp1 of FIG. 2, in which waveform 200 represents the current I1 and the other 202 represents the voltage V1. Referring to FIGS. 2 and 3, when the signal U1 switches the transistor MP1, the current I1 on the package inductance Lp1 varies, as shown by the waveform 200, thereby resulting in ripples of the voltage V1 on the package inductance Lp1, as shown by the waveform 202, and further resulting in the switching noise Snoise on the power line VIN. The greater the variation of the current I1 is, the greater the switching noise Snoise is. Besides, since all the channels 106, 108, . . . , 110 share the common power line VIN, the switching noise Snoise generated on the channel 106 will interfere the other channels 108, . . . , 110.
FIG. 4 further illustrates the influence brought by the switching noise Snoise of FIG. 2, in which waveform 300 represents a threshold Verror1, waveform 302 represents the current-sensing signal ISENSE1, waveform 304 represents the signal U1, waveform 306 represents the switching noise Snoise, waveform 308 represents another threshold Verror2, waveform 310 represents the current-sensing signal ISENSE2, and waveform 312 represents the signal U2. The threshold Verror1 is produced by amplifying the difference between the feedback signal FB1 and a preset reference voltage with an error amplifier, and the threshold Verror2 is also a result of amplifying the difference between the feedback signal FB2 and the preset reference voltage. Taking the channels 106 and 108 for example, under normal operation, when the signal U1 turns to low, the transistor MH1 is turned on and will not be turned off unless the current-sensing signal ISENSE1 rises up to the threshold Verror1, as indicated between time t1 and time t2. Likewise, when the signal U2 turns to low, the transistor MH2 is turned on and will not be turned off unless the current-sensing signal ISENSE2 rises up to the threshold Verror2. However, at time t1, since the transistor MP1 is turned on, the switching noise Snoise is produced, as shown by the waveform 306. When the switching noise Snoise superimposes on the current-sensing signal ISENSE2 through the common power line VIN, as shown by the waveform 310, the channel 108 will perform a misoperation and turn off the transistor MH2 prematurely.
Therefore, it is desired an apparatus and method for preventing a switching converter from misoperation caused by switching noise.